1. Field of the Invention
This invention relates to the field of brain surgery and other intracranial procedures performed on humans and, more specifically, to methods and apparatus for interrelating the positions of noninvasive stereoadapters used in performing presurgical diagnostic procedures and invasive stereotactic headring apparatus used in performing surgical, or other treatment, procedures.
2. Description of the Prior Art
Procedures which involve surgery, radiation or other procedures performed on the brain or other intracranial structures are especially hazardous for the patient, because of the extreme sensitivity of brain tissues, the difficulty in identifying and accessing the particular portion of the brain upon which a procedure is to be performed, and the danger of damaging brain tissues which overlie or surround the portion upon which the procedure is to be performed. The desire for precisely locating and accessing interior portions of the brain and other intracranial structures have lead to the development of the neurosurgical subspecialty of stereotactic surgery or "stereotaxis."
Stereotaxis ordinarily involves the use of an external apparatus attached to the patient's skull during presurgical diagnostic procedures and during surgical procedures. The apparatus provides a grid or framework in fixed position relative to the patient's skull which may be used to establish a coordinate system for locating, in a reproducible manner, the precise position of a lesion or other area within the intracranial area. The fixed framework also provides a structure external to the skull to which measuring devices, surgical instruments and the like can be attached and, by appropriate manipulation, positioned so they can be introduced to exact points within the intracranial structure. Surgical or other procedures then can be performed at an exact, predetermined, point within the brain or other tissue. The object of such devices is, ultimately, to permit safe impact at a predetermined location within the intracranial space for purposes such as excision, surgical biopsy, placement of catheters, installation of devices, removal of cysts, tumors or hematomas, or may involve focusing or direction of laser beams, radiation, magnetism or the like for diagnostic or treatment purposes.
The development of CAT scan technology, magnetic resonance imaging (MRI), angiography, digital subtraction angiography (DSA) and similar diagnostic procedures for producing images of structures contained within tissue has been applied to the field of stereotaxis to produce image-directed stereotaxis. A stereotactic apparatus is used in conjunction with advanced diagnostic imaging procedures to produce internal tissue images keyed to a cartesian or polar coordinate system. When the same stereotactic apparatus is utilized during surgery, it is possible to access a precise position inside the brain identified on the diagnostic images on the basis of the same coordinate system. Such image directed stereotactic procedures involve, generally, the steps of:
(1) establishing a stereotactic space incorporating all areas of the cranial structure under investigation by means of a rigid external framework positioned in fixed relationship to the skull; PA1 (2) performing diagnostic imaging procedures with the framework in place, so that any lesion or other intracranial structure identified by the imaging procedure can be located in precise relationship to the fixed external framework and its position recorded on the basis of a coordinate system related to the stereotactic framework; and PA1 (3) utilizing the same external stereotactic framework and coordinate system during the surgical procedure to guide the surgical instruments, etc., to the precise location inside the cranium where a procedure is to be performed.
Although various stereotactic framework systems are in use throughout the world, the most popular systems are the Radionics Brown-Roberts-Wells (BRW) stereotactic system, the Cosman, Roberts and Wells (CRW) system, and the Elekta Instruments Leksell stereotactic system. The BRW, CRW, Leksell and other systems utilize an external headring which is rigidly attached to the patient's skull by means of four extensible pins, a localizing device with a plurality of vertical and inclined rods which may be attached to the headring during diagnostic procedures and which, in conjunction with computer software developed for the system, can translate CAT scan, MRI, etc., diagnostic imaging information produced with the headring and localizing device in place into X, Y and Z coordinates for any point within the stereotactic space. For the surgical procedure, the fixed headring is left in place, but the localizing device is removed and an arc or other surgical instrument placement device is attached to the headring which permits placement of a probe or other surgical instrument at any point in the intracranial space defined by the X, Y and Z coordinates. For ease of reference, all such stereotactic systems which use an external headring adapted to be rigidly and invasively attached to a patient's skull are referred to herein as "BRW/CRW."
A more detailed explanation of the prior art technology in this area may be obtained from various publications such as, for example, STEREOTACTIC BRAIN BIOPSY, P. T. Chandrasoma, M.D., and Michael L. J. Apuzzo, M.D. (Igaku-Shoin Medical Publishers, Inc. 1989); Heilbrun, M. P. (ed): STEREOTACTIC NEUROSURGERY, Baltimore, Williams & Wilkins, 1988; Lunsford, L. D. (ed): MODERN STEREOTACTIC NEUROSURGERY, Boston, Martinus Nijhoff Publishing, 1988.
Since stereotactic procedures have become increasingly important and widely used in the neurosurgical management of brain tumors and arteriovenous malformations, additional applications for the techniques are being developed. Recent advances include the use of stereotactic techniques in conjunction with linear accelerator therapy for tumor and arteriovenous malformation (AVM) irradiation, and fractionated radiotherapy for the treatment of deep-seated, surgically inaccessible brain tumors. The key to these developments has been the precision with which stereotaxis allows the surgeon to approach intracranial lesions or other areas, regardless of their size or location.
Until recently, for patients undergoing stereotactic procedures, it was necessary that all preoperative imaging procedures be performed on the day of surgery, because localization of a lesion or other intracranial structure was dependent upon extremely precise calculations done with the stereotactic headring in place. Since even the slightest variation in the position of the headring relative to the CAT scan, angiographic study, MRI imaging, etc. would negate the accuracy of the system, it was not possible for the ring to be removed until all the necessary components of the treatment had been completed. Unfortunately, this meant that some patients who required multiple pre-operative studies would be seen early in the morning of the procedure, have the fixed headring applied, spend the better part of the day having imaging studies done with the headring in place, and then begin the operative procedure itself in the late afternoon or evening. This was not only very stressful for the patient, but created difficult scheduling problems for the various medical services and personnel involved.
However, a device recently has been developed by Lauri Laitinen.sup.1 and tested by Dr. Marwan Hariz.sup.2 in Sweden. The Laitinen device, known as the "Laitinen stereoadapter," is noninvasive and is removably attached in an exactly reproducible position to the patient's head by reference to the patient's nose bridge and ears, so that it can be applied, removed and reapplied precisely. The Laitinen stereoadapter incorporates fiducial markers which can be related to CAT scans, magnetic resonance images, DSA or other images to establish an intracranial coordinate system. Since the device also can be applied, removed and reapplied substantially precisely, stereotactic coordinates can be obtained at the time of surgery, with full confidence that the position of the patient's head at the time of surgery is exactly where it was relative to the pre-operative imaging studies. Using the Laitinen stereoadapter, a patient could, for example, have a CAT scan done one day, an angiogram done another day, and the actual surgical procedure performed on a third day. FNT .sup.1 Laitinen, L., Liliequist, B., Fagerlund, M. and Erikson, A. T.: An adapter for computer tomography-guided stereotaxis. Surg. Neurol. 23:559-566, 1985. Laitinen, L.: The Laitinen System. IN: Lunsford, L. D. (ed): Modem Stereotactic Neurosurgery, Boston, Nijhoff, 1988, pp. 99-116. FNT .sup.2 Hariz, M. I.: A Non-invasive Adaptation System for Computed Tomography-Guided Stereotactic Neurosurgery. University of Umea (Sweden), 1990. Hariz, M. I.: Clinical Study on the Accuracy of the Laitinen CT-Guidance System in Functional Stereotactic Neurosurgery. Stereo. Funct. Neurosurg. 56:, 1991.
The Laitinen stereoadapter is compatible with the Laitinen stereotactic system (stereoguide), which utilizes a fixed external arcuate structure similar to a stereotactic headring for supporting surgical and measuring instruments, etc., at the time of surgery. The Laitinen external arc is attached to the patient's skull by means of extensible pins, and keys off of the stereoadapter, to assure accurate placement. Once the fixed external arc is in place, the stereoadapter is removed. Imaging or other diagnostic procedures performed using the Laitinen stereoadapter then identify intracranial structures on the basis of the same coordinate system utilized by the Laitinen system fixed external arc during surgical procedures.
The development of the Laitinen technology has been an important advance in stereotactic surgery for users of the Laitinen stereotactic system, most of whom are in Europe. However, the Laitinen stereoadapter is not compatible with BRW/CRW type stereotactic systems which are more prevalent in the United States. This is in part because the Laitinen and BRW/CRW systems use different baselines for the axes of their coordinate systems and because the BRW/CRW headrings cannot be sufficiently accurately positioned with respect to the Laitinen stereoadapter by any prior art means.